The present invention relates to electro-hydraulic brake systems, and more specifically, the invention relates to an improved brake master cylinder-sensor system and method.
Master cylinders are commonly used in various applications, particularly in automobiles where they control various vehicular systems. For example, braking systems commonly known as brake-by-wire (BBW) or similar systems typically include a master cylinder that is isolated from the braking system. Such BBW systems rely on automatic electric or electric-hydraulic means to remotely activate the brake. Slave cylinders located at the automobile wheels typically actuate a braking process. Furthermore, one or more sensors positioned to monitor vehicle brake pedal position may control the process. The sensors measure pedal movement characteristics and relay this information to the brake system. The information is used to determine the appropriate braking force and is typically proportionate to a brake pedal force.
A potential shortcoming of current automobile master cylinder assemblies relates to positioning the sensors near the brake pedal. Situating the sensors on or near the brake pedal may require additional installation time and cost. Strategies for positioning a Hall effect sensor integral to a master cylinder are known thereby simplifying the packaging of the master cylinder-sensor assembly. The Hall effect sensors are capable of detecting minute perturbations in magnetic fields. These sensors, for example, may be used to precisely measure the movement of a neighboring permanent magnet that moves in response to a brake pedal motion.
The U.S. Pat. No. 4,918,921 issued Apr. 24, 1990 to Leigh-Monstevens et al. is an example of a coaxial push rod and ball screw nut drive for a master cylinder. In the Leigh-Monstevens patent, several forms of master cylinder assemblies are disclosed, including one embodiment for use in a vehicle braking system. In the preferred form, the assembly includes an electrically driven motor, a ball screw, and a piston positioned coaxially within a master cylinder bore. During operation, the motor armature rotates thereby driving the ball screw into the piston and slidably moving the piston within the bore. The assembly may include a Hall effect sensor carried by the master cylinder. As the armature spins, the Hall effect sensor detects passage of a series of rotating circumferentially positioned permanent magnet segments. The linear position of the ball screw and piston are determined based on the rotation count measured by the sensor.
The Leigh-Monstevens patent may disclose a suitable strategy for determining the linear position of a piston within the master cylinder bore. The invention, however, requires a spinning electrical motor armature to rotate magnets in the proximity of, for example, a Hall effect sensor to read piston position. Some master cylinder assemblies do not utilize electrical motors and, thus, cannot detect piston position within the cylinder bore using this strategy. Therefore, it would be desirable to achieve a brake master cylinder capable of integral piston position measurement without the need for an electrical motor that overcomes the aforementioned and other disadvantages.
One aspect of the invention provides a brake master cylinder-sensor system comprising: a master cylinder, a piston slidably positioned in the master cylinder, a magnet positioned on the piston, and a sensor disposed on the master cylinder. A change of piston linear position causes a linear change in a magnetic field position sensed by the sensor, and a brake control signal proportional to the change of linear piston position is generated. The master cylinder may comprise a non-ferrous material. The non-ferrous material may comprise aluminum. The magnet changes linear position in response to a brake pedal movement and may be positioned in a magnetic proximity to the sensor. The magnet may comprise a permanent magnet and the sensor may comprise a Hall effect transducer. The brake control signal may be proportional to a piston linear travel, and the piston linear travel may be proportional to a brake pedal movement. The brake control signal may be sent to a vehicle brake system wherein the vehicle brake system may be activated in proportion to a brake control signal intensity.
Another aspect of the invention provides for a method of operating a brake master cylinder-sensor system comprising: applying a brake pedal force, changing a piston linear position within a master cylinder, determining a change in a linear magnetic field position proportional to the change of the piston linear position, and generating a brake control signal based on the change in the linear magnetic field position. The application of the brake pedal force may result in a linear movement of a piston within the master cylinder. Determining the change in the linear magnetic field position may further comprise repeatedly sensing a magnetic field position with a sensor. A magnet may be positioned in a magnetic proximity to the sensor and may produce the magnetic field.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.